Separation of ethers



Nov. 12, 1968 F. DEAN SEPARATION OF ETHER Filed April 314. 1967 w mmblnvenlor De@ /v United States Patent O 3,410,762 SEPARATION OF ETHERSFred Dean, Norton-on-Tees, England, assignor to Imperial ChemicalIndustries Limited, London, England, a corporation of Great BritainContinuation-impart of application Ser. No. 296,442, July 22, 1963. Thisapplication Apr. 14, 1967, Ser. No. 630,816 Claims priority, applicationGreat Britain, July 27, 1962, 28,940/ 62 Claims. (Ci. 203-64) ABSTRACTOF THE DISCLOSURE High boiling residues produced in the distillation ofcrude alcohols produced by the carbonylation of olenes, are freed fromethers by azeotropic distillation with a lower diol.

This is a continuation-in-part of United States application Ser. No.296,442, tiled on Iuly22, 1963, now abandoned.

This invention relates to the separation of ethers.

It is known that oletines may be reacted with carbon monoxide andhydrogen in the presence of a suitable catalyst for example, a cobaltcontaining catalyst, to give aldehydes and alcohols and that thealdehydes may be subsequently hydrogenated to alcohols. This process isgenerally known as the carbonylation of olenes.

The crude alcohol-containing product of the carbonylation process isusually distilled and the desired alcohols recovered as a distillate,leaving a distillation residue consisting of a mixture of a wide varietyof compounds for example, ethers, higher alcohols and esters. Normallythis distillation residue contains to 90% by volume of ethers in whichthe alkyl groups correspond to the primary product alcohols of thecarbonylation process, i.e., alcohols containing n-I-l carbon atomswhere n is the number of carbon atoms in the olenes carbonylated. Theresidue also contains: 1 to 25 normally 5 to 10%, by volume of CM1alcohols; 10 to 60% of C2n+2 alcohols (dimers) derived by condensationof two primary product alcohols; and esters of the Cn+1 alcohol andcarboxylic acids corresponding to the CM1 alcohol. The C2n+2 alcoholshave a structure in which an alkyl group corresponding to a primaryproduct alcohol is substituted at the alpha-position of the same or adifferent primary product alcohol, e.g., RCH2CH2CHRCH2OH where RCH2CH2OHis the primary product alcohol. In addition the residue contains ethersand esters derived from the C2n+2 alcohols.

A typical product consists of 60% of ethers, 25% of the substitutedalcohols, 10% of the alcohol product and 5% of esters by volume.

When, for example, commercially available mixtures of heptenes arecarbonylated, a wide variety of alcohols are produced, as such heptenesare normally made by reacting propylene with mixtures of butenes. Thealcohol product normally consists of to 25% of mono-methyl heptanolscomprising 3,4,5- and -methyl heptan l-ols, and 75 to 80% of dimethylhexanols comprising mainly 4,5- and 3,4-dimethyl hexanol-l and minoramounts of 3,5-dimethyl hexanol-l.

The distillation residue has commercial value since for example, it canbe oxidised with caustic soda to give acids suitable for the manufactureof paint driers; it is how ever, desirable to remove the ethers beforeapplying this oxidation process.

It is frequently diicult to separate the ethers of the aforementioneddistillation residue because of the large number of compounds presenthaving very similar boiling 3,410,762 Patented Nov. 12, 1968 ICC points.For instance fractional distillation of the distillation residue isusually impracticable or impossible.

The present invention provides a process for separating ethers fromhigh-boiling residues, from which it is difiicult to separate the ethersIby normal distillation, which residues are obtained in the distillationof crude alcohol produced by the carbonylation of olenes, by subjectingthe said residues to azetropic distillation with a diol having 2 to 4carbon atoms.

Residues diiiicult to separate by normal distillation but from whichethers may be suitably separated in accordance with the presentinvention are those boiling above 200 1C. and especially above 250 C. atatmospheric pressure.

Before being subjected to the process of the invention the high boilingresidues may be first distilled to remove as a distillate, any remaininglower boiling alcohols which are the primary alcohol product ot thecarbonylation process.

A variety of diols may be used in the process of the invention examplesbeing ethylene glycol, the propanediols and the butanediols. It ispreferred to use 1:2-propanediol because of its low boiling point.

A small amount of a diol is capable of effecting the separation of arelatively large amount of ethers. The minimum amount of the diolrequired depends upon the dynamic hold-up of the particular distillationcolumn used. Generally speaking the amount of the diol may be 1-20% forexample 10% by volume of the ethers to be separated.

It is very desirable that the azeotropic distillation is conducted underreliux conditions in order to achieve efficient separation of theethers. The reilux ratio required depends on the characteristics of thedistillation apparatus. It may be for example 1:1 but higher or lowerreflux ratios may be used. The reflux may be the azeotrope or azeotropesformed during the distillation or it may be the diol for example diolseparated from the azeotrope.

The distillate leaving the distillation column is condensed to form acondensate which separates into an etherrich layer and a diol-richlayer. The ether-rich layer on cooling may contain a small proportion ofdiol, usually less than 1%, which may be removed for example, by washingwith water, and the ethers then purified by distillation or other means.The diol-rich layer may be returned wholly or in part to thedistillation column as reflux or to the boiler of the distillationcolumn.

The distillation residue containing mainly higher molecular weightalcohols and glycol may be treated to remove the diol for example bydistillation. The remaining material corresponds essentially to thehigher alcohol component of the original residues together with theester component thereof, and a small amount of ethers constitutingnormally at most 5% by volume, and often as little as 1% by volume. Thismaterial is very suitable for oxidation to acids. Such oxidation may besuitably perlformed with caustic soda.

The gure is a diagrammatic illustration of an embodiment of the presentprocess and is labeled to render the figure self-explanatory.

The process of the invention is applicable to the separation of ethersfrom the high-boiling residues obtained by the distillation of crudealcohols produced in the carbonylation of a wide variety of olenes oroleline mixtures which may be aliphatic oletines such as heptenes,di-isobutylene, propylene dimer or alicyclic oleines or aromatic olenes.The high-boiling residues obtained in the carbonylation of two or moredifferent oleine feedstocks may be mixed before treatment according tothe process of the invention.

3 Example l l litre of a distillation residue obtained by distillingcrude iso-octanol produced by the carbonylation of a commercial mixtureof heptenes was introduced into the boiler of a 2-litre glass stillfitted with a 25-plate Oldershaw column. The residue contained 12% byweight of isooctanols (mainly 4,5- and 3,4-dimethyl hexanols-l, withsome 3, 4, 5-, and 6-methyl heptanols), 30% by volume of C16 alcoholscorresponding to the above iso-octanols substituted in the a position byalkyl groups corresponding to the above iso-octanols, for example thealcohol of formula:

8% by volume of predominantly C16 aliphatic esters in which the alcoholand acid moieties are derived from iso-octanols; for example theS-methyl heptyl ester of 3,4-dimethyl hexanoic acid, and 50% by volumeof predominantly C16 aliphatic ethers, having alkyl groups correspondingto the iso-octanols, for example di-4,5-dimeth yl hexyl ether. Thecolumn was attached to a condenser and a magnetic liquid split deviceand there was a cooler and a liquid decanter in the exit line. Theboiler was heated by a heating mantle.

100 ml. iso-octanol were first distilled from the distillation residuesusing a reflux ratio of 10:1. The final still head vapour temperaturewas 225 C.

200 ml. propylene glycol were then added to the contents of the boilerand 30 ml. propylene glycol placed in the decanter. Distillation wasthen continued at a reflux ratio of 1:1 and a still head temperature ofl80-l82 C. The ether/ propylene glycol azeotrope obtained as adistillate contained about 25% by volume of ethers. The aZeotrope whichwas taken off was cooled to ambient temperature and allowed to separatein the decanter into an etherrich layer and a glycol-rich layer whichwas returned directly to the boiler. After 8 hours the distillation ofethers had substantially ceased and the ether layer, which containedless than 1% of propylene glycol, was washed twice with water andseparated. 450 ml. ethers were obtained boiling'within the range 23628lC. and having a hydroxyl value of less than 5 mg. KOH/ gm., an acidvalue of 0.3 mg. KOH/ gm. and an ester value of nil.

The residual liquid remaining in the boiler was then distilled to removepropylene glycol and recover a product corresponding to theaforementioned C16 alcohol and ester components but containing about 5%of ethers, which was then satisfactorily oxidised to acids by means offused caustic soda.

4 Example 2 The process described in Example l was repeated usingethylene glycol instead of propylene glycol. 4801 ml. of ethers wereobtained, leaving a residue containing about 2% of ethers.

I claim:

1. A process in which the high-boiling distillation residue containingethers, alcohols and esters produced by distilling ofr alcohols from theproduct obtained in carbonylating a mixture of heptenes is renderedsuitable for use in the production of paint driers, which processcomprises removing dioctyl ethers from the said residue by azeotropicdistillation with an aliphatic diol having from 2 to 4 carbon atomswhereby said ethers are separated from said residue as an azeotrope withsaid diol.

2. A process for removing aliphatic ethers from highboiling distillationresidues produced by distilling alcohols from a crude product obtainedin carbonylating olenes to produce primary product alcohols, whichresidues comprise from l0 to 90% by volume of aliphatic ethers, thealkyl groups of which ethers correspond to those of said primary productalcohols, l to I25% by Volume of the said primary product alcohols, andl0 to 60% by volume of dimer alcohols in which an alkyl groupcorresponding to the said primary product alcohol is substituted at analpha position of a primary product alcohol, together with esters of thesaid primary product alcohols with carboxylic acids corresponding to thesaid primary product alcohols, which process comprises azeotropicallydistilling said residues with an aliphatic diol having 2 to 4 carbonatoms, whereby said aliphatic ethers are removed from said residue as anazeotrope with said diol.

3. A process according to claim 2 in which the residues boil above 250C., under'atmospheric pressure.

4. A process as claimed in claim 1 in which any lower boiling alcoholswhich are the primary product of the carbonylation process aresubstantially completely removed `by normal distillation prior t-oazeotropic distillation of the residue with the diol.

5. A process as claimed in claim 1 in which the distillate is separatedinto an ether-rich layer and a diol-rich layer, and at least part of thediol-rich layer is returned to a distillation device used in theazeotropic distillation.

References Cited UNITED STATES PATENTS 2,717,271 9/1955 Rowe 260-6162,779,720 l/ 1957 Tanona 260-616 2,802,846 8/ 1957 Mertzweiller 2606382,894,990 7/ 1959 Wennerberg et al. 260-638 2,927,064 3/1960 LuZader etal 203-64 WILBUR L. BASCOMB, JR., Primary Examiner.

